Event~related brain potentials (ERP) were used to study cognitive processes such as short~ and long~term memory, spatial attention and visual search, mental rotation, mental arithmetic, and language comprehension. ERP studies of normal subjects were intended to reveal the brain mechanisms underlying cognition. Studies of patients with neurologic disorders were intended to allow us to characterize better patients~ information processing deficits while providing information on the physiologic mechanisms underlying these cognitive processes. Data collection was completed in ERP studies of dementia Alzheimer's and Parkinson's diseases, HIV disease, and progressive supranuclear palsy (PSP). The results from the HIV and PSP studies indicate that, in the earliest stages of subcortical disease, processing at the cortical level is more affected than processing at the subcortical level (i.e., resembling a cortical dementia). This pattern reverses as the subcortical disease progresses. A follow~up study on the modality specificity of deficits in PSP patients has been completed. Studies of the mechanisms underlying and affecting attentional processes continue and data analysis is complete in two studies, one on how normal controls visually search a spatial array for items previously stored in short~term memory, and the other on the effects of fatigue on attention in patients with chronic fatigue syndrome (CFS) and normal controls. Studies with Dr. Daniel Ruchkin have demonstrated that memory rehearsal processes are marked by large negative slow waves and that different brain areas are invoked to perform verbal and spatial short~term memory rehearsal processes. Additional studies on the nature of short~ and long~term memory deficits in amnestic patients have been completed and data analysis has begun. A study of multiple sclerosis patients revealed that they have a selective deficit in their short~term memory for verbal materials. Data analysis continues on studies of temporal lobectomy patients, Turner's patients, and the maturation of cognitive processes. Studies with Dr. Wolfgang Miltner have been aimed at providing additional data on the neural generator mechanisms underlying cognitive processes. Patient and control data have been used to validate the predictions of Johnson's model of the variables controlling P300 amplitude. These data revealed that, contrary to the widely accepted notion, the P300 is a component whose amplitude represents the simultaneous utilization of a number of cognitive processing "modules." During recognition memory in controls and patients, these modules appear to indicate the presence and functioning of different memory systems.